Rosette prior to dissection, Jan.22, 2011
15 Leaves Removed from a Single C. carduacea Plant
by Bob Harms
The plant chosen for this set of pictures has longer leaves than is typical for C. carduacea, by virtue of its shady and somewhat more moist location. Close inspection shows that the narrowing of the blade is longer only by virtue of the overall leaf length, and actual petioles where present are quite short. Shrinkage with older leaves makes distinguishing petiole from simple leaf narrowing extremely difficult — as is often the case with dried pressed specimens.
Individual leaves arranged by age, oldest (top left) to youngest (bottom right): [A 16th larger leaf (not shown) was also extracted. The remaining stem with 5 youngest leaves is shown at the bottom of this page.]
The length of the narrowed base seems to be correlated with the relative age of the leaf, oldest with longest bases, but not with overall leaf length or width. In general there appears to be little difference in leaf length among the 15. I am tempted to speculate that as newer leaves emerge new growth in the leaves underneath is greater in the petiolar region, pushing the blade toward greater light. (Lengthening of the petiolar area with C. texana does not appear to be restricted to lower/older leaves that might otherwise be covered by newer growth.)
The stem with remaining 5 leaves (keyed a-e, oldest to youngest), an old peduncle (1) and two flower buds (2,3). Note that the stem is barely 6 mm long. So with a total of 21 leaf nodes, the internode length must be < 0.5 mm. A detail viewed from above follows.
Plant Resources Center Home Page — Flora of Texas
— Chaptalia
